1. Field of the Invention
The present invention relates to an optical member inspection apparatus for detecting defective factors of an optical member such as a lens, etc.
2. Description of the Related Art
An optical member such as a lens or a prism is designed so that a luminous flux incoming into the optical member is regularly refracted, advanced in parallel, converged onto a point or line, or diverged. However, if the optical member contains a foreign substance such as yarn waste (so-called fuss) or the like which had been immixed while the optical member is formed, or if the surface of the optical member is scratched during handling thereof by an operator after it had been formed, a luminous flux incoming into the optical member is disturbed and thereby, a desired optical property cannot be obtained.
Therefore, various optical-member inspection apparatuses detecting defective factors of an optical member to automatically decide the quality of an optical member have been proposed so far. For example, Japanese Patent Application Laid-Open No. 10-246706 discloses an optical member inspection apparatus which outputs image data for deciding the quality of an inspection target optical member, by using an imaging optical system and a line sensor arranged on the optical axis of the optical member, and thereby picking up the optical member while rotating the optical member about its optical axis. In a picture shown by the image data obtained by the optical member inspection apparatus, defective factors of the optical member are imaged as bright images in a dark background corresponding to the normal region.
In this case, the inspection target optical member is picked up from a position on its optical axis. Therefore, the lateral face of the optical member (that is, "edge" as for a lens) is imaged as a bright image (which is annular image as for a lens, which is referred to as "edge image") inside of the outer border of the optical member in the picture shown by the image data which is obtained by picking up the optical member. Particularly, in the case that a negative lens having a thick edge (such as a negative meniscus lens) is picked up from the concave side, the width of the edge image increases.
An image processor of the optical-member inspection apparatus distinguishes a region corresponding to the optical member within image data, based on the position of a lateral image in the image data and cuts out only region inside the lateral image as an object region of image-processing which is called "inspection target region" herein after.
As a holder for holding an inspection target optical member in an optical-member inspection apparatus, an annular holder of which internal surface is formed with inward flange or spot facing for supporting the entire outer margin of the inspection target optical member is often adopted so as to be able to securely hold the inspection target optical member regardless of its edge thickness. FIG. 17 is a sectional view showing such a conventional holder. The conventional holder shown in FIG. 17 is made of a cylindrical member 100. On the inner edge of the opening at the upper end 101 of the cylindrical member 100, a spot facing portion 102 which is lowered by one step is formed so as to support the outer margin of the optical member.
However, when the outer margin of the inspection target optical member is mounted on the inward flange or spot facing of the holder having the above shape, illumination light is shaded by the inward flange or spot facing and thereby, the illumination light does not reach the lateral face of the inspection target optical member. As a result, no rays come into an image pickup device because rays are reflected on the lateral face and therefore, a lateral image is not formed in a picture shown by image data. If the lateral image is not imaged in the picture shown by the image data, it is impossible to securely identify a region corresponding to the inspection target optical member in the image data. That bring a mistake that unnecessary noises are contained in inspection results due to regions other than the proper region corresponding to the inspection target optical member being included in an inspection target region, or a mistake that defective factor is overlooked by excluding a part or the whole of the proper region corresponding to the inspection target optical member from the inspection target region. If the above mistakes occur, it is impossible to accurately decide the quality of the inspection target optical member. In case that only one holder having specific diameter for one size of optical member is used, the above problem is not serious because the range of proper region can be preset. However, in case that plurality of holders respectively having various diameters are exchangeably used (that is, in case that optical members having various diameters are inspected), the above problem becomes very serious because the range of inspection target region must be actively set in accordance with acquired image data itself.
Furthermore, according to the conventional holder shown in FIG. 17, an object serving as an aim for lowering an inspection target optical member to set it to a holder is only the spot facing portion 102 itself. Therefore, to set the inspection target optical member to the holder, an operator is liable to carelessly hit the inspection target optical member against the upper end 101 of the cylindrical member 100 to scratch a surface of the inspection target optical member because the operator does not know a right course of letdown of the inspection target optical member. Otherwise, the operator may waste a lot of time by carefully performing operations so as not to scratch the surface of the inspection target optical member. Moreover, when the width of the lateral face (edge as for a lens) of an inspection target optical member is narrow, the lateral face (edge) completely enters the spot facing 102. In this case, the operator cannot pick up the optical member in the spot facing 102 with his or her fingers. Therefore, the operator may scratch the surface of the inspection target optical member by a jig or waste the working time, with intent to take out the optical member from the spot facing 102 by using the jig.